The stress-buffering effect of perceived support is explored in a large panel survey of adult female twins. The analysis begins by documenting a significant interaction between perceived support and acute stress in predicting DSM-III-R major depression. Various hypotheses are investigated to explain this interaction. These include the possibilities that the interaction is due to a stress-buffering effect of perceived support which is mediated by received support, that perceived support promotes either the increased use or the increased effectiveness of certain coping strategies, or that there is some underlying genetic factor that affects both the perception of support and adjustment to stress. No evidence was found for any of these hypotheses. The paper closes with a discussion of directions for future research aimed at explaining the interaction between perceived support and acute stress.